import java.util.Scanner;

public class Homework5 {
    //递归求 1 + 2 + 3 + ... + 10
    public static int func(int a){
        if(a==0){
            return 0;
        }
        return a+func(a-1);
    }
    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        int a = input.nextInt();
        int b = func(a);
        System.out.println(b);
    }
}
